The subject matter of this application relates to the subject matter of U.S. Pat. No. 5,427,580, entitled "Phased Chain Assemblies," issued Jun. 27, 1995, the subject matter of which is incorporated herein by reference.
The present invention relates generally to power transmission chains. The invention has particular application to power transmission chains of the inverted tooth or silent chain variety, which are used in automotive engine timing applications, and also can have automotive applications in the transfer of power from a torque converter to a transmission or in a transfer case of a four-wheel drive vehicle.
One type of power transmission chain is referred to as silent chain. Such chain is formed of interleaved sets of inverted tooth links. A set or row of links is assembled from several links positioned alongside of or adjacent to each other. The links are connected by pivot means, which are typically round pins received in a pair of apertures.
Conventional silent chains typically include both guide links and inverted tooth links. The guide links are positioned on the outside edges of alternate rows of links. The guide links typically act to position the chain laterally on the sprocket. Guide links typically do not mesh with the sprocket.
The inverted tooth links, or sprocket engaging links, provide the transfer of power between the chain and the sprocket. Each inverted tooth link typically includes a pair of apertures and a pair of depending toes or teeth. Each toe is defined by an inside flank and an outside flank. The inside flanks are typically joined at a crotch. The inverted tooth links are typically designed so that the links contact the sprocket teeth to transfer power between the chain assembly and the sprocket. The inverted tooth links or driving links contact the sprocket teeth along their inside link flanks or their outside link flanks or combinations of both flanks. The contacts between the links and sprocket teeth can be of the type which provide a power transfer, or can be of the nature of an incidental contact, or can include root contact or side contact.
A conventional silent chain drive is comprised of an endless silent chain wrapped about at least two sprockets supported by shafts. Rotation of a driving sprocket causes power transmission through the chain and consequent movement of a driven sprocket. In an engine timing drive application, the driving sprocket is mounted on the engine crankshaft and the driven sprocket is mounted on the engine camshaft.
Chain assemblies are typically constructed of links of a matching pitch length. In round pin silent chains, the pitch length is the distance between the centers or center points of the pair of round apertures on each link. The links of the chain are typically provided with the same or approximately the same (within manufacturing tolerances) pitch length. In turn, the sprockets associated with this chain are constructed of a pitch length that matches the chain pitch length. The pitch length of a sprocket is conventionally measured as the distance between the adjoining sprocket teeth as measured along the sprocket pitch circle. In such a chain and sprocket system, the links of each of the successive rows of the chain will initially contact each successive sprocket tooth as the chain enters the sprocket and then proceeds to seat in the sprocket.
Chain assemblies of the prior art have included double pitch roller chains. In such chains, the links span two adjacent sprocket teeth so that the pins are separated by two sprocket teeth. It is believed that the prior art may have included double pitch silent chains, but only in the form of low speed conveyor chain, and not for any high-speed automotive applications.
The present invention has particular application to chain assemblies in which the chains or sprockets are offset, or phased, to modify the impact noise spectrum and chordal action noise spectrum. In a typical phased chain system, a single chain assembly is divided into, or replaced by, two side-by-side chains that are phased or offset by one-half pitch. In one embodiment of the present invention, the chain link structure is utilized on two chains that are in side-by-side relationship. The chain link has a pitch length that is approximately twice the pitch length of the associated sprocket. Two such chains are placed in side-by-side, but phased relationship. The system achieves phasing without the need to circumferentially offset the sprockets with respect to one another. The successive rows of each chain initially contact every other successive tooth of the associated sprocket. The contacting of every other tooth provides the phasing of the chain to sprocket contacts.
Noise is associated with chain drives. Noise is generated by a variety of sources, but in silent chain drives it can be caused, in part, by the impact sound generated by the collision of the chain and the sprocket at the onset of meshing. The loudness of the impact sound is affected by, among other things, the impact velocity between the chain and the sprocket and the mass of chain links contacting the sprocket at a particular moment or time increment.
Many efforts have been made to decrease the overall noise level and pitch frequency noise distribution in automotive chain drives to minimize the objectionable effects of the pure sonic tones. Several of those efforts are discussed in the above-mentioned U.S. Pat. No. 5,427,580. The present invention finds application along with some of the noise reduction concepts discussed in the above-mentioned application, including randomization and phasing of the chain assemblies. However, the present invention has broader applications to chain systems that include, for example, non-phased sprockets.
Phasing the chain and sprocket relationship can reduce the number of chain links (or mass) impacting the sprocket during a given time increment. Similarly, phasing the chain and sprocket relationship can alter or phase the chordal action or articulation of the chain and sprocket.
However, the use of a phased chain system often involves two chains that are placed in side-by-side and phased relation. The two side-by-side sprockets are then circumferentially offset by approximately one-half pitch. Such a system requires manufacture and assembly of sprocket systems that provide the described circumferential offset. The present invention, in one embodiment, avoids the need for circumferentially offset sprockets. This is accomplished by utilizing two chains in side-by-side relationship with the links of the chains having a pitch length approximately twice the length of the sprocket pitch and the chains being positioned on the sprockets with their pins being displaced by one half pitch.